CareerCup

Here is the solution


class A
{
public:
A(int i)
{

}
private:
A() {}
~A() {}

public:
static A* instance()
{
return new A();
}

static void free_instance(A* a)
{
delete a;
}
};

int _tmain(int argc, _TCHAR* argv[])
{
A a1(2); // error C2248: 'A::~A' : cannot access private member declared in class 'A'

A* aa = A::instance();

A::free_instance(aa);
}

Declare private destructor for class A....

@Tito
Isn't it possible by making class static?

add a explicit keyword before the class constructor. Then the constructor with single argument wouldn't go for implicit conversion.

Add default parameters with the private ctor for A.
like "A(int x=0,int y=0){};"

you just put the class definition in a local scope

Can't we just declare the new constructor to be private? also is this is abstract class, cause in the first place we cannot create object of it anywaz

Create another class lock with private constructor.
Drive your class "A" with it.

class lock
{
  private:
  lock()
  {}
};
class A: public lock
{
  // Any constructor
};

This disables the instantiation of your class "A"

How about this? Create another class (Foo) and have its no argument constructor private. Derive the given class A from the above create Foo class. However this will prevent any constructors of class A to work. I am not sure what the intent is.

class A 
{
public:
	A(int i)
	{

	}
private:
	A() {}
	~A() {}

public:
	static A* instance()
	{
		return new A();
	}

	static void free_instance(A* a)
	{
		delete a;
	}
};

int _tmain(int argc, _TCHAR* argv[])
{
	A a1(2); //  error C2248: 'A::~A' : cannot access private member declared in class 'A'

	A* aa = A::instance();

	A::free_instance(aa);
}

add a protected destructor

i think creating at least one pure virtual function makes the creation of object for the class impossible.

As @Ashutosh explained, use non-copyable base class. Refer boost for details.

class A {
int a_;
~A() {}

public:
A(int a) :a_(a) {}
void destroy() { delete this; }
};

int main()
{
A a(1); //can't call as destructor private
A *ptr = new A(1);
ptr->destroy();
return 0;
}

Try abstract class. In this case try define destructor as pure virtual